In hard disk drives (HDD) and magnetic optical disks, as the tendency toward higher recording densities increases and the recording area per bit becomes smaller, technology for writing to, and reading from, a smaller area of a recording medium is demanded. However, for continuous media which are used in conventional HDDs, when the areal or bit density is increased to the order of terabits/square inch, the recording area per bit is as small as approx. 20 square nanometers and the problem of thermal disturbance is significant. Therefore, in commercial high density recording devices, a material with high anisotropy energy has been used to prevent thermal disturbance and efforts toward finer grains and reduction of intergrain interaction have been made to prevent the phenomenon of side writing. Recently, for higher recording densities, studies of discrete track media and patterned media have been conducted in which discrete patterns are made in the recording layers of the media in order to reduce noise associated with side writing phenomena. However, since the magnetic energy per recorded bit should be above a predetermined level for the purpose of preventing thermal disturbance, a large magnetic field would be required in a conventional recording system.
The write head uses a magnetic field which is generated from a magnetic pole by energizing a coil on the principle of an electromagnet. If the bit density is very high, the phenomenon of magnetic field insufficiency might be apparent. In order to solve this problem, heat-assisted magnetic recording has been considered in which the head is provided with a light source, such as a laser, and a material whose coercivity changes with heat is used for the recording medium, and during recording laser irradiation is done to raise the medium's temperature.
As a technique similar to the above, JP-A No. 91801/2003 proposes a recording system which uses a recording layer with a multilayered structure consisting of a layer of material with high anisotropy energy and a layer of photoexcited ferromagnetic material, and the recording layer's coercivity is reduced by magnetic material exchange coupling. This phenomenon is limited to the particular materials described in JP-A No. 255707/1996.